2                       T H E  /proc   F I L E S Y S T E M
   4/proc/sys         Terrehon Bowden <>        October 7 1999
   5                  Bodo Bauer <>
   72.4.x update      Jorge Nerin <>      November 14 2000
   8move /proc/sys    Shen Feng <>                 April 1 2009
  10Version 1.3                                              Kernel version 2.2.12
  11                                              Kernel version 2.4.0-test11-pre4
  13fixes/update part 1.1  Stefani Seibold <>       June 9 2009
  15Table of Contents
  18  0     Preface
  19  0.1   Introduction/Credits
  20  0.2   Legal Stuff
  22  1     Collecting System Information
  23  1.1   Process-Specific Subdirectories
  24  1.2   Kernel data
  25  1.3   IDE devices in /proc/ide
  26  1.4   Networking info in /proc/net
  27  1.5   SCSI info
  28  1.6   Parallel port info in /proc/parport
  29  1.7   TTY info in /proc/tty
  30  1.8   Miscellaneous kernel statistics in /proc/stat
  31  1.9   Ext4 file system parameters
  33  2     Modifying System Parameters
  35  3     Per-Process Parameters
  36  3.1   /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj - Adjust the oom-killer
  37                                                                score
  38  3.2   /proc/<pid>/oom_score - Display current oom-killer score
  39  3.3   /proc/<pid>/io - Display the IO accounting fields
  40  3.4   /proc/<pid>/coredump_filter - Core dump filtering settings
  41  3.5   /proc/<pid>/mountinfo - Information about mounts
  42  3.6   /proc/<pid>/comm  & /proc/<pid>/task/<tid>/comm
  43  3.7   /proc/<pid>/task/<tid>/children - Information about task children
  44  3.8   /proc/<pid>/fdinfo/<fd> - Information about opened file
  45  3.9   /proc/<pid>/map_files - Information about memory mapped files
  46  3.10  /proc/<pid>/timerslack_ns - Task timerslack value
  48  4     Configuring procfs
  49  4.1   Mount options
  550.1 Introduction/Credits
  58This documentation is  part of a soon (or  so we hope) to be  released book on
  59the SuSE  Linux distribution. As  there is  no complete documentation  for the
  60/proc file system and we've used  many freely available sources to write these
  61chapters, it  seems only fair  to give the work  back to the  Linux community.
  62This work is  based on the 2.2.*  kernel version and the  upcoming 2.4.*. I'm
  63afraid it's still far from complete, but we  hope it will be useful. As far as
  64we know, it is the first 'all-in-one' document about the /proc file system. It
  65is focused  on the Intel  x86 hardware,  so if you  are looking for  PPC, ARM,
  66SPARC, AXP, etc., features, you probably  won't find what you are looking for.
  67It also only covers IPv4 networking, not IPv6 nor other protocols - sorry. But
  68additions and patches  are welcome and will  be added to this  document if you
  69mail them to Bodo.
  71We'd like  to  thank Alan Cox, Rik van Riel, and Alexey Kuznetsov and a lot of
  72other people for help compiling this documentation. We'd also like to extend a
  73special thank  you to Andi Kleen for documentation, which we relied on heavily
  74to create  this  document,  as well as the additional information he provided.
  75Thanks to  everybody  else  who contributed source or docs to the Linux kernel
  76and helped create a great piece of software... :)
  78If you  have  any comments, corrections or additions, please don't hesitate to
  79contact Bodo  Bauer  at  We'll  be happy to add them to this
  82The   latest   version    of   this   document   is    available   online   at
  85If  the above  direction does  not works  for you,  you could  try the  kernel
  86mailing  list  at  and/or try  to  reach  me  at
  890.2 Legal Stuff
  92We don't  guarantee  the  correctness  of this document, and if you come to us
  93complaining about  how  you  screwed  up  your  system  because  of  incorrect
  94documentation, we won't feel responsible...
 101In This Chapter
 103* Investigating  the  properties  of  the  pseudo  file  system  /proc and its
 104  ability to provide information on the running Linux system
 105* Examining /proc's structure
 106* Uncovering  various  information  about the kernel and the processes running
 107  on the system
 111The proc  file  system acts as an interface to internal data structures in the
 112kernel. It  can  be  used to obtain information about the system and to change
 113certain kernel parameters at runtime (sysctl).
 115First, we'll  take  a  look  at the read-only parts of /proc. In Chapter 2, we
 116show you how you can use /proc/sys to change settings.
 1181.1 Process-Specific Subdirectories
 121The directory  /proc  contains  (among other things) one subdirectory for each
 122process running on the system, which is named after the process ID (PID).
 124The link  self  points  to  the  process reading the file system. Each process
 125subdirectory has the entries listed in Table 1-1.
 128Table 1-1: Process specific entries in /proc
 130 File           Content
 131 clear_refs     Clears page referenced bits shown in smaps output
 132 cmdline        Command line arguments
 133 cpu            Current and last cpu in which it was executed   (2.4)(smp)
 134 cwd            Link to the current working directory
 135 environ        Values of environment variables
 136 exe            Link to the executable of this process
 137 fd             Directory, which contains all file descriptors
 138 maps           Memory maps to executables and library files    (2.4)
 139 mem            Memory held by this process
 140 root           Link to the root directory of this process
 141 stat           Process status
 142 statm          Process memory status information
 143 status         Process status in human readable form
 144 wchan          Present with CONFIG_KALLSYMS=y: it shows the kernel function
 145                symbol the task is blocked in - or "0" if not blocked.
 146 pagemap        Page table
 147 stack          Report full stack trace, enable via CONFIG_STACKTRACE
 148 smaps          a extension based on maps, showing the memory consumption of
 149                each mapping and flags associated with it
 150 numa_maps      an extension based on maps, showing the memory locality and
 151                binding policy as well as mem usage (in pages) of each mapping.
 154For example, to get the status information of a process, all you have to do is
 155read the file /proc/PID/status:
 157  >cat /proc/self/status
 158  Name:   cat
 159  State:  R (running)
 160  Tgid:   5452
 161  Pid:    5452
 162  PPid:   743
 163  TracerPid:      0                                             (2.4)
 164  Uid:    501     501     501     501
 165  Gid:    100     100     100     100
 166  FDSize: 256
 167  Groups: 100 14 16
 168  VmPeak:     5004 kB
 169  VmSize:     5004 kB
 170  VmLck:         0 kB
 171  VmHWM:       476 kB
 172  VmRSS:       476 kB
 173  RssAnon:             352 kB
 174  RssFile:             120 kB
 175  RssShmem:              4 kB
 176  VmData:      156 kB
 177  VmStk:        88 kB
 178  VmExe:        68 kB
 179  VmLib:      1412 kB
 180  VmPTE:        20 kb
 181  VmSwap:        0 kB
 182  HugetlbPages:          0 kB
 183  Threads:        1
 184  SigQ:   0/28578
 185  SigPnd: 0000000000000000
 186  ShdPnd: 0000000000000000
 187  SigBlk: 0000000000000000
 188  SigIgn: 0000000000000000
 189  SigCgt: 0000000000000000
 190  CapInh: 00000000fffffeff
 191  CapPrm: 0000000000000000
 192  CapEff: 0000000000000000
 193  CapBnd: ffffffffffffffff
 194  Seccomp:        0
 195  voluntary_ctxt_switches:        0
 196  nonvoluntary_ctxt_switches:     1
 198This shows you nearly the same information you would get if you viewed it with
 199the ps  command.  In  fact,  ps  uses  the  proc  file  system  to  obtain its
 200information.  But you get a more detailed  view of the  process by reading the
 201file /proc/PID/status. It fields are described in table 1-2.
 203The  statm  file  contains  more  detailed  information about the process
 204memory usage. Its seven fields are explained in Table 1-3.  The stat file
 205contains details information about the process itself.  Its fields are
 206explained in Table 1-4.
 208(for SMP CONFIG users)
 209For making accounting scalable, RSS related information are handled in an
 210asynchronous manner and the value may not be very precise. To see a precise
 211snapshot of a moment, you can see /proc/<pid>/smaps file and scan page table.
 212It's slow but very precise.
 214Table 1-2: Contents of the status files (as of 4.1)
 216 Field                       Content
 217 Name                        filename of the executable
 218 State                       state (R is running, S is sleeping, D is sleeping
 219                             in an uninterruptible wait, Z is zombie,
 220                             T is traced or stopped)
 221 Tgid                        thread group ID
 222 Ngid                        NUMA group ID (0 if none)
 223 Pid                         process id
 224 PPid                        process id of the parent process
 225 TracerPid                   PID of process tracing this process (0 if not)
 226 Uid                         Real, effective, saved set, and  file system UIDs
 227 Gid                         Real, effective, saved set, and  file system GIDs
 228 Umask                       file mode creation mask
 229 FDSize                      number of file descriptor slots currently allocated
 230 Groups                      supplementary group list
 231 NStgid                      descendant namespace thread group ID hierarchy
 232 NSpid                       descendant namespace process ID hierarchy
 233 NSpgid                      descendant namespace process group ID hierarchy
 234 NSsid                       descendant namespace session ID hierarchy
 235 VmPeak                      peak virtual memory size
 236 VmSize                      total program size
 237 VmLck                       locked memory size
 238 VmHWM                       peak resident set size ("high water mark")
 239 VmRSS                       size of memory portions. It contains the three
 240                             following parts (VmRSS = RssAnon + RssFile + RssShmem)
 241 RssAnon                     size of resident anonymous memory
 242 RssFile                     size of resident file mappings
 243 RssShmem                    size of resident shmem memory (includes SysV shm,
 244                             mapping of tmpfs and shared anonymous mappings)
 245 VmData                      size of private data segments
 246 VmStk                       size of stack segments
 247 VmExe                       size of text segment
 248 VmLib                       size of shared library code
 249 VmPTE                       size of page table entries
 250 VmPMD                       size of second level page tables
 251 VmSwap                      amount of swap used by anonymous private data
 252                             (shmem swap usage is not included)
 253 HugetlbPages                size of hugetlb memory portions
 254 Threads                     number of threads
 255 SigQ                        number of signals queued/max. number for queue
 256 SigPnd                      bitmap of pending signals for the thread
 257 ShdPnd                      bitmap of shared pending signals for the process
 258 SigBlk                      bitmap of blocked signals
 259 SigIgn                      bitmap of ignored signals
 260 SigCgt                      bitmap of caught signals
 261 CapInh                      bitmap of inheritable capabilities
 262 CapPrm                      bitmap of permitted capabilities
 263 CapEff                      bitmap of effective capabilities
 264 CapBnd                      bitmap of capabilities bounding set
 265 Seccomp                     seccomp mode, like prctl(PR_GET_SECCOMP, ...)
 266 Cpus_allowed                mask of CPUs on which this process may run
 267 Cpus_allowed_list           Same as previous, but in "list format"
 268 Mems_allowed                mask of memory nodes allowed to this process
 269 Mems_allowed_list           Same as previous, but in "list format"
 270 voluntary_ctxt_switches     number of voluntary context switches
 271 nonvoluntary_ctxt_switches  number of non voluntary context switches
 274Table 1-3: Contents of the statm files (as of 2.6.8-rc3)
 276 Field    Content
 277 size     total program size (pages)            (same as VmSize in status)
 278 resident size of memory portions (pages)       (same as VmRSS in status)
 279 shared   number of pages that are shared       (i.e. backed by a file, same
 280                                                as RssFile+RssShmem in status)
 281 trs      number of pages that are 'code'       (not including libs; broken,
 282                                                        includes data segment)
 283 lrs      number of pages of library            (always 0 on 2.6)
 284 drs      number of pages of data/stack         (including libs; broken,
 285                                                        includes library text)
 286 dt       number of dirty pages                 (always 0 on 2.6)
 290Table 1-4: Contents of the stat files (as of 2.6.30-rc7)
 292 Field          Content
 293  pid           process id
 294  tcomm         filename of the executable
 295  state         state (R is running, S is sleeping, D is sleeping in an
 296                uninterruptible wait, Z is zombie, T is traced or stopped)
 297  ppid          process id of the parent process
 298  pgrp          pgrp of the process
 299  sid           session id
 300  tty_nr        tty the process uses
 301  tty_pgrp      pgrp of the tty
 302  flags         task flags
 303  min_flt       number of minor faults
 304  cmin_flt      number of minor faults with child's
 305  maj_flt       number of major faults
 306  cmaj_flt      number of major faults with child's
 307  utime         user mode jiffies
 308  stime         kernel mode jiffies
 309  cutime        user mode jiffies with child's
 310  cstime        kernel mode jiffies with child's
 311  priority      priority level
 312  nice          nice level
 313  num_threads   number of threads
 314  it_real_value (obsolete, always 0)
 315  start_time    time the process started after system boot
 316  vsize         virtual memory size
 317  rss           resident set memory size
 318  rsslim        current limit in bytes on the rss
 319  start_code    address above which program text can run
 320  end_code      address below which program text can run
 321  start_stack   address of the start of the main process stack
 322  esp           current value of ESP
 323  eip           current value of EIP
 324  pending       bitmap of pending signals
 325  blocked       bitmap of blocked signals
 326  sigign        bitmap of ignored signals
 327  sigcatch      bitmap of caught signals
 328  0             (place holder, used to be the wchan address, use /proc/PID/wchan instead)
 329  0             (place holder)
 330  0             (place holder)
 331  exit_signal   signal to send to parent thread on exit
 332  task_cpu      which CPU the task is scheduled on
 333  rt_priority   realtime priority
 334  policy        scheduling policy (man sched_setscheduler)
 335  blkio_ticks   time spent waiting for block IO
 336  gtime         guest time of the task in jiffies
 337  cgtime        guest time of the task children in jiffies
 338  start_data    address above which program data+bss is placed
 339  end_data      address below which program data+bss is placed
 340  start_brk     address above which program heap can be expanded with brk()
 341  arg_start     address above which program command line is placed
 342  arg_end       address below which program command line is placed
 343  env_start     address above which program environment is placed
 344  env_end       address below which program environment is placed
 345  exit_code     the thread's exit_code in the form reported by the waitpid system call
 348The /proc/PID/maps file containing the currently mapped memory regions and
 349their access permissions.
 351The format is:
 353address           perms offset  dev   inode      pathname
 35508048000-08049000 r-xp 00000000 03:00 8312       /opt/test
 35608049000-0804a000 rw-p 00001000 03:00 8312       /opt/test
 3570804a000-0806b000 rw-p 00000000 00:00 0          [heap]
 358a7cb1000-a7cb2000 ---p 00000000 00:00 0
 359a7cb2000-a7eb2000 rw-p 00000000 00:00 0
 360a7eb2000-a7eb3000 ---p 00000000 00:00 0
 361a7eb3000-a7ed5000 rw-p 00000000 00:00 0
 362a7ed5000-a8008000 r-xp 00000000 03:00 4222       /lib/
 363a8008000-a800a000 r--p 00133000 03:00 4222       /lib/
 364a800a000-a800b000 rw-p 00135000 03:00 4222       /lib/
 365a800b000-a800e000 rw-p 00000000 00:00 0
 366a800e000-a8022000 r-xp 00000000 03:00 14462      /lib/
 367a8022000-a8023000 r--p 00013000 03:00 14462      /lib/
 368a8023000-a8024000 rw-p 00014000 03:00 14462      /lib/
 369a8024000-a8027000 rw-p 00000000 00:00 0
 370a8027000-a8043000 r-xp 00000000 03:00 8317       /lib/
 371a8043000-a8044000 r--p 0001b000 03:00 8317       /lib/
 372a8044000-a8045000 rw-p 0001c000 03:00 8317       /lib/
 373aff35000-aff4a000 rw-p 00000000 00:00 0          [stack]
 374ffffe000-fffff000 r-xp 00000000 00:00 0          [vdso]
 376where "address" is the address space in the process that it occupies, "perms"
 377is a set of permissions:
 379 r = read
 380 w = write
 381 x = execute
 382 s = shared
 383 p = private (copy on write)
 385"offset" is the offset into the mapping, "dev" is the device (major:minor), and
 386"inode" is the inode  on that device.  0 indicates that  no inode is associated
 387with the memory region, as the case would be with BSS (uninitialized data).
 388The "pathname" shows the name associated file for this mapping.  If the mapping
 389is not associated with a file:
 391 [heap]                   = the heap of the program
 392 [stack]                  = the stack of the main process
 393 [vdso]                   = the "virtual dynamic shared object",
 394                            the kernel system call handler
 396 or if empty, the mapping is anonymous.
 398The /proc/PID/task/TID/maps is a view of the virtual memory from the viewpoint
 399of the individual tasks of a process. In this file you will see a mapping marked
 400as [stack] if that task sees it as a stack. Hence, for the example above, the
 401task-level map, i.e. /proc/PID/task/TID/maps for thread 1001 will look like this:
 40308048000-08049000 r-xp 00000000 03:00 8312       /opt/test
 40408049000-0804a000 rw-p 00001000 03:00 8312       /opt/test
 4050804a000-0806b000 rw-p 00000000 00:00 0          [heap]
 406a7cb1000-a7cb2000 ---p 00000000 00:00 0
 407a7cb2000-a7eb2000 rw-p 00000000 00:00 0
 408a7eb2000-a7eb3000 ---p 00000000 00:00 0
 409a7eb3000-a7ed5000 rw-p 00000000 00:00 0          [stack]
 410a7ed5000-a8008000 r-xp 00000000 03:00 4222       /lib/
 411a8008000-a800a000 r--p 00133000 03:00 4222       /lib/
 412a800a000-a800b000 rw-p 00135000 03:00 4222       /lib/
 413a800b000-a800e000 rw-p 00000000 00:00 0
 414a800e000-a8022000 r-xp 00000000 03:00 14462      /lib/
 415a8022000-a8023000 r--p 00013000 03:00 14462      /lib/
 416a8023000-a8024000 rw-p 00014000 03:00 14462      /lib/
 417a8024000-a8027000 rw-p 00000000 00:00 0
 418a8027000-a8043000 r-xp 00000000 03:00 8317       /lib/
 419a8043000-a8044000 r--p 0001b000 03:00 8317       /lib/
 420a8044000-a8045000 rw-p 0001c000 03:00 8317       /lib/
 421aff35000-aff4a000 rw-p 00000000 00:00 0
 422ffffe000-fffff000 r-xp 00000000 00:00 0          [vdso]
 424The /proc/PID/smaps is an extension based on maps, showing the memory
 425consumption for each of the process's mappings. For each of mappings there
 426is a series of lines such as the following:
 42808048000-080bc000 r-xp 00000000 03:02 13130      /bin/bash
 429Size:               1084 kB
 430Rss:                 892 kB
 431Pss:                 374 kB
 432Shared_Clean:        892 kB
 433Shared_Dirty:          0 kB
 434Private_Clean:         0 kB
 435Private_Dirty:         0 kB
 436Referenced:          892 kB
 437Anonymous:             0 kB
 438AnonHugePages:         0 kB
 439ShmemPmdMapped:        0 kB
 440Shared_Hugetlb:        0 kB
 441Private_Hugetlb:       0 kB
 442Swap:                  0 kB
 443SwapPss:               0 kB
 444KernelPageSize:        4 kB
 445MMUPageSize:           4 kB
 446Locked:                0 kB
 447VmFlags: rd ex mr mw me dw
 449the first of these lines shows the same information as is displayed for the
 450mapping in /proc/PID/maps.  The remaining lines show the size of the mapping
 451(size), the amount of the mapping that is currently resident in RAM (RSS), the
 452process' proportional share of this mapping (PSS), the number of clean and
 453dirty private pages in the mapping.
 455The "proportional set size" (PSS) of a process is the count of pages it has
 456in memory, where each page is divided by the number of processes sharing it.
 457So if a process has 1000 pages all to itself, and 1000 shared with one other
 458process, its PSS will be 1500.
 459Note that even a page which is part of a MAP_SHARED mapping, but has only
 460a single pte mapped, i.e.  is currently used by only one process, is accounted
 461as private and not as shared.
 462"Referenced" indicates the amount of memory currently marked as referenced or
 464"Anonymous" shows the amount of memory that does not belong to any file.  Even
 465a mapping associated with a file may contain anonymous pages: when MAP_PRIVATE
 466and a page is modified, the file page is replaced by a private anonymous copy.
 467"AnonHugePages" shows the ammount of memory backed by transparent hugepage.
 468"ShmemPmdMapped" shows the ammount of shared (shmem/tmpfs) memory backed by
 469huge pages.
 470"Shared_Hugetlb" and "Private_Hugetlb" show the ammounts of memory backed by
 471hugetlbfs page which is *not* counted in "RSS" or "PSS" field for historical
 472reasons. And these are not included in {Shared,Private}_{Clean,Dirty} field.
 473"Swap" shows how much would-be-anonymous memory is also used, but out on swap.
 474For shmem mappings, "Swap" includes also the size of the mapped (and not
 475replaced by copy-on-write) part of the underlying shmem object out on swap.
 476"SwapPss" shows proportional swap share of this mapping. Unlike "Swap", this
 477does not take into account swapped out page of underlying shmem objects.
 478"Locked" indicates whether the mapping is locked in memory or not.
 480"VmFlags" field deserves a separate description. This member represents the kernel
 481flags associated with the particular virtual memory area in two letter encoded
 482manner. The codes are the following:
 483    rd  - readable
 484    wr  - writeable
 485    ex  - executable
 486    sh  - shared
 487    mr  - may read
 488    mw  - may write
 489    me  - may execute
 490    ms  - may share
 491    gd  - stack segment growns down
 492    pf  - pure PFN range
 493    dw  - disabled write to the mapped file
 494    lo  - pages are locked in memory
 495    io  - memory mapped I/O area
 496    sr  - sequential read advise provided
 497    rr  - random read advise provided
 498    dc  - do not copy area on fork
 499    de  - do not expand area on remapping
 500    ac  - area is accountable
 501    nr  - swap space is not reserved for the area
 502    ht  - area uses huge tlb pages
 503    ar  - architecture specific flag
 504    dd  - do not include area into core dump
 505    sd  - soft-dirty flag
 506    mm  - mixed map area
 507    hg  - huge page advise flag
 508    nh  - no-huge page advise flag
 509    mg  - mergable advise flag
 511Note that there is no guarantee that every flag and associated mnemonic will
 512be present in all further kernel releases. Things get changed, the flags may
 513be vanished or the reverse -- new added.
 515This file is only present if the CONFIG_MMU kernel configuration option is
 518The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG
 519bits on both physical and virtual pages associated with a process, and the
 520soft-dirty bit on pte (see Documentation/vm/soft-dirty.txt for details).
 521To clear the bits for all the pages associated with the process
 522    > echo 1 > /proc/PID/clear_refs
 524To clear the bits for the anonymous pages associated with the process
 525    > echo 2 > /proc/PID/clear_refs
 527To clear the bits for the file mapped pages associated with the process
 528    > echo 3 > /proc/PID/clear_refs
 530To clear the soft-dirty bit
 531    > echo 4 > /proc/PID/clear_refs
 533To reset the peak resident set size ("high water mark") to the process's
 534current value:
 535    > echo 5 > /proc/PID/clear_refs
 537Any other value written to /proc/PID/clear_refs will have no effect.
 539The /proc/pid/pagemap gives the PFN, which can be used to find the pageflags
 540using /proc/kpageflags and number of times a page is mapped using
 541/proc/kpagecount. For detailed explanation, see Documentation/vm/pagemap.txt.
 543The /proc/pid/numa_maps is an extension based on maps, showing the memory
 544locality and binding policy, as well as the memory usage (in pages) of
 545each mapping. The output follows a general format where mapping details get
 546summarized separated by blank spaces, one mapping per each file line:
 548address   policy    mapping details
 55000400000 default file=/usr/local/bin/app mapped=1 active=0 N3=1 kernelpagesize_kB=4
 55100600000 default file=/usr/local/bin/app anon=1 dirty=1 N3=1 kernelpagesize_kB=4
 5523206000000 default file=/lib64/ mapped=26 mapmax=6 N0=24 N3=2 kernelpagesize_kB=4
 553320621f000 default file=/lib64/ anon=1 dirty=1 N3=1 kernelpagesize_kB=4
 5543206220000 default file=/lib64/ anon=1 dirty=1 N3=1 kernelpagesize_kB=4
 5553206221000 default anon=1 dirty=1 N3=1 kernelpagesize_kB=4
 5563206800000 default file=/lib64/ mapped=59 mapmax=21 active=55 N0=41 N3=18 kernelpagesize_kB=4
 557320698b000 default file=/lib64/
 5583206b8a000 default file=/lib64/ anon=2 dirty=2 N3=2 kernelpagesize_kB=4
 5593206b8e000 default file=/lib64/ anon=1 dirty=1 N3=1 kernelpagesize_kB=4
 5603206b8f000 default anon=3 dirty=3 active=1 N3=3 kernelpagesize_kB=4
 5617f4dc10a2000 default anon=3 dirty=3 N3=3 kernelpagesize_kB=4
 5627f4dc10b4000 default anon=2 dirty=2 active=1 N3=2 kernelpagesize_kB=4
 5637f4dc1200000 default file=/anon_hugepage\040(deleted) huge anon=1 dirty=1 N3=1 kernelpagesize_kB=2048
 5647fff335f0000 default stack anon=3 dirty=3 N3=3 kernelpagesize_kB=4
 5657fff3369d000 default mapped=1 mapmax=35 active=0 N3=1 kernelpagesize_kB=4
 568"address" is the starting address for the mapping;
 569"policy" reports the NUMA memory policy set for the mapping (see vm/numa_memory_policy.txt);
 570"mapping details" summarizes mapping data such as mapping type, page usage counters,
 571node locality page counters (N0 == node0, N1 == node1, ...) and the kernel page
 572size, in KB, that is backing the mapping up.
 5741.2 Kernel data
 577Similar to  the  process entries, the kernel data files give information about
 578the running kernel. The files used to obtain this information are contained in
 579/proc and  are  listed  in Table 1-5. Not all of these will be present in your
 580system. It  depends  on the kernel configuration and the loaded modules, which
 581files are there, and which are missing.
 583Table 1-5: Kernel info in /proc
 585 File        Content                                           
 586 apm         Advanced power management info                    
 587 buddyinfo   Kernel memory allocator information (see text)     (2.5)
 588 bus         Directory containing bus specific information     
 589 cmdline     Kernel command line                               
 590 cpuinfo     Info about the CPU                                
 591 devices     Available devices (block and character)           
 592 dma         Used DMS channels                                 
 593 filesystems Supported filesystems                             
 594 driver      Various drivers grouped here, currently rtc (2.4)
 595 execdomains Execdomains, related to security                   (2.4)
 596 fb          Frame Buffer devices                               (2.4)
 597 fs          File system parameters, currently nfs/exports      (2.4)
 598 ide         Directory containing info about the IDE subsystem 
 599 interrupts  Interrupt usage                                   
 600 iomem       Memory map                                         (2.4)
 601 ioports     I/O port usage                                    
 602 irq         Masks for irq to cpu affinity                      (2.4)(smp?)
 603 isapnp      ISA PnP (Plug&Play) Info                           (2.4)
 604 kcore       Kernel core image (can be ELF or A.OUT(deprecated in 2.4))   
 605 kmsg        Kernel messages                                   
 606 ksyms       Kernel symbol table                               
 607 loadavg     Load average of last 1, 5 & 15 minutes                
 608 locks       Kernel locks                                      
 609 meminfo     Memory info                                       
 610 misc        Miscellaneous                                     
 611 modules     List of loaded modules                            
 612 mounts      Mounted filesystems                               
 613 net         Networking info (see text)                        
 614 pagetypeinfo Additional page allocator information (see text)  (2.5)
 615 partitions  Table of partitions known to the system           
 616 pci         Deprecated info of PCI bus (new way -> /proc/bus/pci/,
 617             decoupled by lspci                                 (2.4)
 618 rtc         Real time clock                                   
 619 scsi        SCSI info (see text)                              
 620 slabinfo    Slab pool info                                    
 621 softirqs    softirq usage
 622 stat        Overall statistics                                
 623 swaps       Swap space utilization                            
 624 sys         See chapter 2                                     
 625 sysvipc     Info of SysVIPC Resources (msg, sem, shm)          (2.4)
 626 tty         Info of tty drivers
 627 uptime      Wall clock since boot, combined idle time of all cpus
 628 version     Kernel version                                    
 629 video       bttv info of video resources                       (2.4)
 630 vmallocinfo Show vmalloced areas
 633You can,  for  example,  check  which interrupts are currently in use and what
 634they are used for by looking in the file /proc/interrupts:
 636  > cat /proc/interrupts 
 637             CPU0        
 638    0:    8728810          XT-PIC  timer 
 639    1:        895          XT-PIC  keyboard 
 640    2:          0          XT-PIC  cascade 
 641    3:     531695          XT-PIC  aha152x 
 642    4:    2014133          XT-PIC  serial 
 643    5:      44401          XT-PIC  pcnet_cs 
 644    8:          2          XT-PIC  rtc 
 645   11:          8          XT-PIC  i82365 
 646   12:     182918          XT-PIC  PS/2 Mouse 
 647   13:          1          XT-PIC  fpu 
 648   14:    1232265          XT-PIC  ide0 
 649   15:          7          XT-PIC  ide1 
 650  NMI:          0 
 652In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the
 653output of a SMP machine):
 655  > cat /proc/interrupts 
 657             CPU0       CPU1       
 658    0:    1243498    1214548    IO-APIC-edge  timer
 659    1:       8949       8958    IO-APIC-edge  keyboard
 660    2:          0          0          XT-PIC  cascade
 661    5:      11286      10161    IO-APIC-edge  soundblaster
 662    8:          1          0    IO-APIC-edge  rtc
 663    9:      27422      27407    IO-APIC-edge  3c503
 664   12:     113645     113873    IO-APIC-edge  PS/2 Mouse
 665   13:          0          0          XT-PIC  fpu
 666   14:      22491      24012    IO-APIC-edge  ide0
 667   15:       2183       2415    IO-APIC-edge  ide1
 668   17:      30564      30414   IO-APIC-level  eth0
 669   18:        177        164   IO-APIC-level  bttv
 670  NMI:    2457961    2457959 
 671  LOC:    2457882    2457881 
 672  ERR:       2155
 674NMI is incremented in this case because every timer interrupt generates a NMI
 675(Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups.
 677LOC is the local interrupt counter of the internal APIC of every CPU.
 679ERR is incremented in the case of errors in the IO-APIC bus (the bus that
 680connects the CPUs in a SMP system. This means that an error has been detected,
 681the IO-APIC automatically retry the transmission, so it should not be a big
 682problem, but you should read the SMP-FAQ.
 684In 2.6.2* /proc/interrupts was expanded again.  This time the goal was for
 685/proc/interrupts to display every IRQ vector in use by the system, not
 686just those considered 'most important'.  The new vectors are:
 688  THR -- interrupt raised when a machine check threshold counter
 689  (typically counting ECC corrected errors of memory or cache) exceeds
 690  a configurable threshold.  Only available on some systems.
 692  TRM -- a thermal event interrupt occurs when a temperature threshold
 693  has been exceeded for the CPU.  This interrupt may also be generated
 694  when the temperature drops back to normal.
 696  SPU -- a spurious interrupt is some interrupt that was raised then lowered
 697  by some IO device before it could be fully processed by the APIC.  Hence
 698  the APIC sees the interrupt but does not know what device it came from.
 699  For this case the APIC will generate the interrupt with a IRQ vector
 700  of 0xff. This might also be generated by chipset bugs.
 702  RES, CAL, TLB -- rescheduling, call and TLB flush interrupts are
 703  sent from one CPU to another per the needs of the OS.  Typically,
 704  their statistics are used by kernel developers and interested users to
 705  determine the occurrence of interrupts of the given type.
 707The above IRQ vectors are displayed only when relevant.  For example,
 708the threshold vector does not exist on x86_64 platforms.  Others are
 709suppressed when the system is a uniprocessor.  As of this writing, only
 710i386 and x86_64 platforms support the new IRQ vector displays.
 712Of some interest is the introduction of the /proc/irq directory to 2.4.
 713It could be used to set IRQ to CPU affinity, this means that you can "hook" an
 714IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the
 715irq subdir is one subdir for each IRQ, and two files; default_smp_affinity and
 718For example 
 719  > ls /proc/irq/
 720  0  10  12  14  16  18  2  4  6  8  prof_cpu_mask
 721  1  11  13  15  17  19  3  5  7  9  default_smp_affinity
 722  > ls /proc/irq/0/
 723  smp_affinity
 725smp_affinity is a bitmask, in which you can specify which CPUs can handle the
 726IRQ, you can set it by doing:
 728  > echo 1 > /proc/irq/10/smp_affinity
 730This means that only the first CPU will handle the IRQ, but you can also echo
 7315 which means that only the first and third CPU can handle the IRQ.
 733The contents of each smp_affinity file is the same by default:
 735  > cat /proc/irq/0/smp_affinity
 736  ffffffff
 738There is an alternate interface, smp_affinity_list which allows specifying
 739a cpu range instead of a bitmask:
 741  > cat /proc/irq/0/smp_affinity_list
 742  1024-1031
 744The default_smp_affinity mask applies to all non-active IRQs, which are the
 745IRQs which have not yet been allocated/activated, and hence which lack a
 746/proc/irq/[0-9]* directory.
 748The node file on an SMP system shows the node to which the device using the IRQ
 749reports itself as being attached. This hardware locality information does not
 750include information about any possible driver locality preference.
 752prof_cpu_mask specifies which CPUs are to be profiled by the system wide
 753profiler. Default value is ffffffff (all cpus if there are only 32 of them).
 755The way IRQs are routed is handled by the IO-APIC, and it's Round Robin
 756between all the CPUs which are allowed to handle it. As usual the kernel has
 757more info than you and does a better job than you, so the defaults are the
 758best choice for almost everyone.  [Note this applies only to those IO-APIC's
 759that support "Round Robin" interrupt distribution.]
 761There are  three  more  important subdirectories in /proc: net, scsi, and sys.
 762The general  rule  is  that  the  contents,  or  even  the  existence of these
 763directories, depend  on your kernel configuration. If SCSI is not enabled, the
 764directory scsi  may  not  exist. The same is true with the net, which is there
 765only when networking support is present in the running kernel.
 767The slabinfo  file  gives  information  about  memory usage at the slab level.
 768Linux uses  slab  pools for memory management above page level in version 2.2.
 769Commonly used  objects  have  their  own  slab  pool (such as network buffers,
 770directory cache, and so on).
 774> cat /proc/buddyinfo
 776Node 0, zone      DMA      0      4      5      4      4      3 ...
 777Node 0, zone   Normal      1      0      0      1    101      8 ...
 778Node 0, zone  HighMem      2      0      0      1      1      0 ...
 780External fragmentation is a problem under some workloads, and buddyinfo is a
 781useful tool for helping diagnose these problems.  Buddyinfo will give you a 
 782clue as to how big an area you can safely allocate, or why a previous
 783allocation failed.
 785Each column represents the number of pages of a certain order which are 
 786available.  In this case, there are 0 chunks of 2^0*PAGE_SIZE available in 
 787ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE 
 788available in ZONE_NORMAL, etc... 
 790More information relevant to external fragmentation can be found in
 793> cat /proc/pagetypeinfo
 794Page block order: 9
 795Pages per block:  512
 797Free pages count per migrate type at order       0      1      2      3      4      5      6      7      8      9     10
 798Node    0, zone      DMA, type    Unmovable      0      0      0      1      1      1      1      1      1      1      0
 799Node    0, zone      DMA, type  Reclaimable      0      0      0      0      0      0      0      0      0      0      0
 800Node    0, zone      DMA, type      Movable      1      1      2      1      2      1      1      0      1      0      2
 801Node    0, zone      DMA, type      Reserve      0      0      0      0      0      0      0      0      0      1      0
 802Node    0, zone      DMA, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
 803Node    0, zone    DMA32, type    Unmovable    103     54     77      1      1      1     11      8      7      1      9
 804Node    0, zone    DMA32, type  Reclaimable      0      0      2      1      0      0      0      0      1      0      0
 805Node    0, zone    DMA32, type      Movable    169    152    113     91     77     54     39     13      6      1    452
 806Node    0, zone    DMA32, type      Reserve      1      2      2      2      2      0      1      1      1      1      0
 807Node    0, zone    DMA32, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
 809Number of blocks type     Unmovable  Reclaimable      Movable      Reserve      Isolate
 810Node 0, zone      DMA            2            0            5            1            0
 811Node 0, zone    DMA32           41            6          967            2            0
 813Fragmentation avoidance in the kernel works by grouping pages of different
 814migrate types into the same contiguous regions of memory called page blocks.
 815A page block is typically the size of the default hugepage size e.g. 2MB on
 816X86-64. By keeping pages grouped based on their ability to move, the kernel
 817can reclaim pages within a page block to satisfy a high-order allocation.
 819The pagetypinfo begins with information on the size of a page block. It
 820then gives the same type of information as buddyinfo except broken down
 821by migrate-type and finishes with details on how many page blocks of each
 822type exist.
 824If min_free_kbytes has been tuned correctly (recommendations made by hugeadm
 825from libhugetlbfs, one can
 826make an estimate of the likely number of huge pages that can be allocated
 827at a given point in time. All the "Movable" blocks should be allocatable
 828unless memory has been mlock()'d. Some of the Reclaimable blocks should
 829also be allocatable although a lot of filesystem metadata may have to be
 830reclaimed to achieve this.
 836Provides information about distribution and utilization of memory.  This
 837varies by architecture and compile options.  The following is from a
 83816GB PIII, which has highmem enabled.  You may not have all of these fields.
 840> cat /proc/meminfo
 842MemTotal:     16344972 kB
 843MemFree:      13634064 kB
 844MemAvailable: 14836172 kB
 845Buffers:          3656 kB
 846Cached:        1195708 kB
 847SwapCached:          0 kB
 848Active:         891636 kB
 849Inactive:      1077224 kB
 850HighTotal:    15597528 kB
 851HighFree:     13629632 kB
 852LowTotal:       747444 kB
 853LowFree:          4432 kB
 854SwapTotal:           0 kB
 855SwapFree:            0 kB
 856Dirty:             968 kB
 857Writeback:           0 kB
 858AnonPages:      861800 kB
 859Mapped:         280372 kB
 860Shmem:             644 kB
 861Slab:           284364 kB
 862SReclaimable:   159856 kB
 863SUnreclaim:     124508 kB
 864PageTables:      24448 kB
 865NFS_Unstable:        0 kB
 866Bounce:              0 kB
 867WritebackTmp:        0 kB
 868CommitLimit:   7669796 kB
 869Committed_AS:   100056 kB
 870VmallocTotal:   112216 kB
 871VmallocUsed:       428 kB
 872VmallocChunk:   111088 kB
 873AnonHugePages:   49152 kB
 874ShmemHugePages:      0 kB
 875ShmemPmdMapped:      0 kB
 878    MemTotal: Total usable ram (i.e. physical ram minus a few reserved
 879              bits and the kernel binary code)
 880     MemFree: The sum of LowFree+HighFree
 881MemAvailable: An estimate of how much memory is available for starting new
 882              applications, without swapping. Calculated from MemFree,
 883              SReclaimable, the size of the file LRU lists, and the low
 884              watermarks in each zone.
 885              The estimate takes into account that the system needs some
 886              page cache to function well, and that not all reclaimable
 887              slab will be reclaimable, due to items being in use. The
 888              impact of those factors will vary from system to system.
 889     Buffers: Relatively temporary storage for raw disk blocks
 890              shouldn't get tremendously large (20MB or so)
 891      Cached: in-memory cache for files read from the disk (the
 892              pagecache).  Doesn't include SwapCached
 893  SwapCached: Memory that once was swapped out, is swapped back in but
 894              still also is in the swapfile (if memory is needed it
 895              doesn't need to be swapped out AGAIN because it is already
 896              in the swapfile. This saves I/O)
 897      Active: Memory that has been used more recently and usually not
 898              reclaimed unless absolutely necessary.
 899    Inactive: Memory which has been less recently used.  It is more
 900              eligible to be reclaimed for other purposes
 901   HighTotal:
 902    HighFree: Highmem is all memory above ~860MB of physical memory
 903              Highmem areas are for use by userspace programs, or
 904              for the pagecache.  The kernel must use tricks to access
 905              this memory, making it slower to access than lowmem.
 906    LowTotal:
 907     LowFree: Lowmem is memory which can be used for everything that
 908              highmem can be used for, but it is also available for the
 909              kernel's use for its own data structures.  Among many
 910              other things, it is where everything from the Slab is
 911              allocated.  Bad things happen when you're out of lowmem.
 912   SwapTotal: total amount of swap space available
 913    SwapFree: Memory which has been evicted from RAM, and is temporarily
 914              on the disk
 915       Dirty: Memory which is waiting to get written back to the disk
 916   Writeback: Memory which is actively being written back to the disk
 917   AnonPages: Non-file backed pages mapped into userspace page tables
 918AnonHugePages: Non-file backed huge pages mapped into userspace page tables
 919      Mapped: files which have been mmaped, such as libraries
 920       Shmem: Total memory used by shared memory (shmem) and tmpfs
 921ShmemHugePages: Memory used by shared memory (shmem) and tmpfs allocated
 922              with huge pages
 923ShmemPmdMapped: Shared memory mapped into userspace with huge pages
 924        Slab: in-kernel data structures cache
 925SReclaimable: Part of Slab, that might be reclaimed, such as caches
 926  SUnreclaim: Part of Slab, that cannot be reclaimed on memory pressure
 927  PageTables: amount of memory dedicated to the lowest level of page
 928              tables.
 929NFS_Unstable: NFS pages sent to the server, but not yet committed to stable
 930              storage
 931      Bounce: Memory used for block device "bounce buffers"
 932WritebackTmp: Memory used by FUSE for temporary writeback buffers
 933 CommitLimit: Based on the overcommit ratio ('vm.overcommit_ratio'),
 934              this is the total amount of  memory currently available to
 935              be allocated on the system. This limit is only adhered to
 936              if strict overcommit accounting is enabled (mode 2 in
 937              'vm.overcommit_memory').
 938              The CommitLimit is calculated with the following formula:
 939              CommitLimit = ([total RAM pages] - [total huge TLB pages]) *
 940                             overcommit_ratio / 100 + [total swap pages]
 941              For example, on a system with 1G of physical RAM and 7G
 942              of swap with a `vm.overcommit_ratio` of 30 it would
 943              yield a CommitLimit of 7.3G.
 944              For more details, see the memory overcommit documentation
 945              in vm/overcommit-accounting.
 946Committed_AS: The amount of memory presently allocated on the system.
 947              The committed memory is a sum of all of the memory which
 948              has been allocated by processes, even if it has not been
 949              "used" by them as of yet. A process which malloc()'s 1G
 950              of memory, but only touches 300M of it will show up as
 951              using 1G. This 1G is memory which has been "committed" to
 952              by the VM and can be used at any time by the allocating
 953              application. With strict overcommit enabled on the system
 954              (mode 2 in 'vm.overcommit_memory'),allocations which would
 955              exceed the CommitLimit (detailed above) will not be permitted.
 956              This is useful if one needs to guarantee that processes will
 957              not fail due to lack of memory once that memory has been
 958              successfully allocated.
 959VmallocTotal: total size of vmalloc memory area
 960 VmallocUsed: amount of vmalloc area which is used
 961VmallocChunk: largest contiguous block of vmalloc area which is free
 967Provides information about vmalloced/vmaped areas. One line per area,
 968containing the virtual address range of the area, size in bytes,
 969caller information of the creator, and optional information depending
 970on the kind of area :
 972 pages=nr    number of pages
 973 phys=addr   if a physical address was specified
 974 ioremap     I/O mapping (ioremap() and friends)
 975 vmalloc     vmalloc() area
 976 vmap        vmap()ed pages
 977 user        VM_USERMAP area
 978 vpages      buffer for pages pointers was vmalloced (huge area)
 979 N<node>=nr  (Only on NUMA kernels)
 980             Number of pages allocated on memory node <node>
 982> cat /proc/vmallocinfo
 9830xffffc20000000000-0xffffc20000201000 2101248 alloc_large_system_hash+0x204 ...
 984  /0x2c0 pages=512 vmalloc N0=128 N1=128 N2=128 N3=128
 9850xffffc20000201000-0xffffc20000302000 1052672 alloc_large_system_hash+0x204 ...
 986  /0x2c0 pages=256 vmalloc N0=64 N1=64 N2=64 N3=64
 9870xffffc20000302000-0xffffc20000304000    8192 acpi_tb_verify_table+0x21/0x4f...
 988  phys=7fee8000 ioremap
 9890xffffc20000304000-0xffffc20000307000   12288 acpi_tb_verify_table+0x21/0x4f...
 990  phys=7fee7000 ioremap
 9910xffffc2000031d000-0xffffc2000031f000    8192 init_vdso_vars+0x112/0x210
 9920xffffc2000031f000-0xffffc2000032b000   49152 cramfs_uncompress_init+0x2e ...
 993  /0x80 pages=11 vmalloc N0=3 N1=3 N2=2 N3=3
 9940xffffc2000033a000-0xffffc2000033d000   12288 sys_swapon+0x640/0xac0      ...
 995  pages=2 vmalloc N1=2
 9960xffffc20000347000-0xffffc2000034c000   20480 xt_alloc_table_info+0xfe ...
 997  /0x130 [x_tables] pages=4 vmalloc N0=4
 9980xffffffffa0000000-0xffffffffa000f000   61440 sys_init_module+0xc27/0x1d00 ...
 999   pages=14 vmalloc N2=14
10000xffffffffa000f000-0xffffffffa0014000   20480 sys_init_module+0xc27/0x1d00 ...
1001   pages=4 vmalloc N1=4
10020xffffffffa0014000-0xffffffffa0017000   12288 sys_init_module+0xc27/0x1d00 ...
1003   pages=2 vmalloc N1=2
10040xffffffffa0017000-0xffffffffa0022000   45056 sys_init_module+0xc27/0x1d00 ...
1005   pages=10 vmalloc N0=10
1011Provides counts of softirq handlers serviced since boot time, for each cpu.
1013> cat /proc/softirqs
1014                CPU0       CPU1       CPU2       CPU3
1015      HI:          0          0          0          0
1016   TIMER:      27166      27120      27097      27034
1017  NET_TX:          0          0          0         17
1018  NET_RX:         42          0          0         39
1019   BLOCK:          0          0        107       1121
1020 TASKLET:          0          0          0        290
1021   SCHED:      27035      26983      26971      26746
1022 HRTIMER:          0          0          0          0
1023     RCU:       1678       1769       2178       2250
10261.3 IDE devices in /proc/ide
1029The subdirectory /proc/ide contains information about all IDE devices of which
1030the kernel  is  aware.  There is one subdirectory for each IDE controller, the
1031file drivers  and a link for each IDE device, pointing to the device directory
1032in the controller specific subtree.
1034The file  drivers  contains general information about the drivers used for the
1035IDE devices:
1037  > cat /proc/ide/drivers
1038  ide-cdrom version 4.53
1039  ide-disk version 1.08
1041More detailed  information  can  be  found  in  the  controller  specific
1042subdirectories. These  are  named  ide0,  ide1  and  so  on.  Each  of  these
1043directories contains the files shown in table 1-6.
1046Table 1-6: IDE controller info in  /proc/ide/ide?
1048 File    Content                                 
1049 channel IDE channel (0 or 1)                    
1050 config  Configuration (only for PCI/IDE bridge) 
1051 mate    Mate name                               
1052 model   Type/Chipset of IDE controller          
1055Each device  connected  to  a  controller  has  a separate subdirectory in the
1056controllers directory.  The  files  listed in table 1-7 are contained in these
1060Table 1-7: IDE device information
1062 File             Content                                    
1063 cache            The cache                                  
1064 capacity         Capacity of the medium (in 512Byte blocks) 
1065 driver           driver and version                         
1066 geometry         physical and logical geometry              
1067 identify         device identify block                      
1068 media            media type                                 
1069 model            device identifier                          
1070 settings         device setup                               
1071 smart_thresholds IDE disk management thresholds             
1072 smart_values     IDE disk management values                 
1075The most  interesting  file is settings. This file contains a nice overview of
1076the drive parameters:
1078  # cat /proc/ide/ide0/hda/settings 
1079  name                    value           min             max             mode 
1080  ----                    -----           ---             ---             ---- 
1081  bios_cyl                526             0               65535           rw 
1082  bios_head               255             0               255             rw 
1083  bios_sect               63              0               63              rw 
1084  breada_readahead        4               0               127             rw 
1085  bswap                   0               0               1               r 
1086  file_readahead          72              0               2097151         rw 
1087  io_32bit                0               0               3               rw 
1088  keepsettings            0               0               1               rw 
1089  max_kb_per_request      122             1               127             rw 
1090  multcount               0               0               8               rw 
1091  nice1                   1               0               1               rw 
1092  nowerr                  0               0               1               rw 
1093  pio_mode                write-only      0               255             w 
1094  slow                    0               0               1               rw 
1095  unmaskirq               0               0               1               rw 
1096  using_dma               0               0               1               rw 
10991.4 Networking info in /proc/net
1102The subdirectory  /proc/net  follows  the  usual  pattern. Table 1-8 shows the
1103additional values  you  get  for  IP  version 6 if you configure the kernel to
1104support this. Table 1-9 lists the files and their meaning.
1107Table 1-8: IPv6 info in /proc/net
1109 File       Content                                               
1110 udp6       UDP sockets (IPv6)                                    
1111 tcp6       TCP sockets (IPv6)                                    
1112 raw6       Raw device statistics (IPv6)                          
1113 igmp6      IP multicast addresses, which this host joined (IPv6) 
1114 if_inet6   List of IPv6 interface addresses                      
1115 ipv6_route Kernel routing table for IPv6                         
1116 rt6_stats  Global IPv6 routing tables statistics                 
1117 sockstat6  Socket statistics (IPv6)                              
1118 snmp6      Snmp data (IPv6)                                      
1122Table 1-9: Network info in /proc/net
1124 File          Content                                                         
1125 arp           Kernel  ARP table                                               
1126 dev           network devices with statistics                                 
1127 dev_mcast     the Layer2 multicast groups a device is listening too
1128               (interface index, label, number of references, number of bound
1129               addresses). 
1130 dev_stat      network device status                                           
1131 ip_fwchains   Firewall chain linkage                                          
1132 ip_fwnames    Firewall chain names                                            
1133 ip_masq       Directory containing the masquerading tables                    
1134 ip_masquerade Major masquerading table                                        
1135 netstat       Network statistics                                              
1136 raw           raw device statistics                                           
1137 route         Kernel routing table                                            
1138 rpc           Directory containing rpc info                                   
1139 rt_cache      Routing cache                                                   
1140 snmp          SNMP data                                                       
1141 sockstat      Socket statistics                                               
1142 tcp           TCP  sockets                                                    
1143 udp           UDP sockets                                                     
1144 unix          UNIX domain sockets                                             
1145 wireless      Wireless interface data (Wavelan etc)                           
1146 igmp          IP multicast addresses, which this host joined                  
1147 psched        Global packet scheduler parameters.                             
1148 netlink       List of PF_NETLINK sockets                                      
1149 ip_mr_vifs    List of multicast virtual interfaces                            
1150 ip_mr_cache   List of multicast routing cache                                 
1153You can  use  this  information  to see which network devices are available in
1154your system and how much traffic was routed over those devices:
1156  > cat /proc/net/dev 
1157  Inter-|Receive                                                   |[... 
1158   face |bytes    packets errs drop fifo frame compressed multicast|[... 
1159      lo:  908188   5596     0    0    0     0          0         0 [...         
1160    ppp0:15475140  20721   410    0    0   410          0         0 [...  
1161    eth0:  614530   7085     0    0    0     0          0         1 [... 
1163  ...] Transmit 
1164  ...] bytes    packets errs drop fifo colls carrier compressed 
1165  ...]  908188     5596    0    0    0     0       0          0 
1166  ...] 1375103    17405    0    0    0     0       0          0 
1167  ...] 1703981     5535    0    0    0     3       0          0 
1169In addition, each Channel Bond interface has its own directory.  For
1170example, the bond0 device will have a directory called /proc/net/bond0/.
1171It will contain information that is specific to that bond, such as the
1172current slaves of the bond, the link status of the slaves, and how
1173many times the slaves link has failed.
11751.5 SCSI info
1178If you  have  a  SCSI  host adapter in your system, you'll find a subdirectory
1179named after  the driver for this adapter in /proc/scsi. You'll also see a list
1180of all recognized SCSI devices in /proc/scsi:
1182  >cat /proc/scsi/scsi 
1183  Attached devices: 
1184  Host: scsi0 Channel: 00 Id: 00 Lun: 00 
1185    Vendor: IBM      Model: DGHS09U          Rev: 03E0 
1186    Type:   Direct-Access                    ANSI SCSI revision: 03 
1187  Host: scsi0 Channel: 00 Id: 06 Lun: 00 
1188    Vendor: PIONEER  Model: CD-ROM DR-U06S   Rev: 1.04 
1189    Type:   CD-ROM                           ANSI SCSI revision: 02 
1192The directory  named  after  the driver has one file for each adapter found in
1193the system.  These  files  contain information about the controller, including
1194the used  IRQ  and  the  IO  address range. The amount of information shown is
1195dependent on  the adapter you use. The example shows the output for an Adaptec
1196AHA-2940 SCSI adapter:
1198  > cat /proc/scsi/aic7xxx/0 
1200  Adaptec AIC7xxx driver version: 5.1.19/3.2.4 
1201  Compile Options: 
1202    TCQ Enabled By Default : Disabled 
1203    AIC7XXX_PROC_STATS     : Disabled 
1204    AIC7XXX_RESET_DELAY    : 5 
1205  Adapter Configuration: 
1206             SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter 
1207                             Ultra Wide Controller 
1208      PCI MMAPed I/O Base: 0xeb001000 
1209   Adapter SEEPROM Config: SEEPROM found and used. 
1210        Adaptec SCSI BIOS: Enabled 
1211                      IRQ: 10 
1212                     SCBs: Active 0, Max Active 2, 
1213                           Allocated 15, HW 16, Page 255 
1214               Interrupts: 160328 
1215        BIOS Control Word: 0x18b6 
1216     Adapter Control Word: 0x005b 
1217     Extended Translation: Enabled 
1218  Disconnect Enable Flags: 0xffff 
1219       Ultra Enable Flags: 0x0001 
1220   Tag Queue Enable Flags: 0x0000 
1221  Ordered Queue Tag Flags: 0x0000 
1222  Default Tag Queue Depth: 8 
1223      Tagged Queue By Device array for aic7xxx host instance 0: 
1224        {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255} 
1225      Actual queue depth per device for aic7xxx host instance 0: 
1226        {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1} 
1227  Statistics: 
1228  (scsi0:0:0:0) 
1229    Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8 
1230    Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0) 
1231    Total transfers 160151 (74577 reads and 85574 writes) 
1232  (scsi0:0:6:0) 
1233    Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15 
1234    Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0) 
1235    Total transfers 0 (0 reads and 0 writes) 
12381.6 Parallel port info in /proc/parport
1241The directory  /proc/parport  contains information about the parallel ports of
1242your system.  It  has  one  subdirectory  for  each port, named after the port
1243number (0,1,2,...).
1245These directories contain the four files shown in Table 1-10.
1248Table 1-10: Files in /proc/parport
1250 File      Content                                                             
1251 autoprobe Any IEEE-1284 device ID information that has been acquired.         
1252 devices   list of the device drivers using that port. A + will appear by the
1253           name of the device currently using the port (it might not appear
1254           against any). 
1255 hardware  Parallel port's base address, IRQ line and DMA channel.             
1256 irq       IRQ that parport is using for that port. This is in a separate
1257           file to allow you to alter it by writing a new value in (IRQ
1258           number or none). 
12611.7 TTY info in /proc/tty
1264Information about  the  available  and actually used tty's can be found in the
1265directory /proc/tty.You'll  find  entries  for drivers and line disciplines in
1266this directory, as shown in Table 1-11.
1269Table 1-11: Files in /proc/tty
1271 File          Content                                        
1272 drivers       list of drivers and their usage                
1273 ldiscs        registered line disciplines                    
1274 driver/serial usage statistic and status of single tty lines 
1277To see  which  tty's  are  currently in use, you can simply look into the file
1280  > cat /proc/tty/drivers 
1281  pty_slave            /dev/pts      136   0-255 pty:slave 
1282  pty_master           /dev/ptm      128   0-255 pty:master 
1283  pty_slave            /dev/ttyp       3   0-255 pty:slave 
1284  pty_master           /dev/pty        2   0-255 pty:master 
1285  serial               /dev/cua        5   64-67 serial:callout 
1286  serial               /dev/ttyS       4   64-67 serial 
1287  /dev/tty0            /dev/tty0       4       0 system:vtmaster 
1288  /dev/ptmx            /dev/ptmx       5       2 system 
1289  /dev/console         /dev/console    5       1 system:console 
1290  /dev/tty             /dev/tty        5       0 system:/dev/tty 
1291  unknown              /dev/tty        4    1-63 console 
12941.8 Miscellaneous kernel statistics in /proc/stat
1297Various pieces   of  information about  kernel activity  are  available in the
1298/proc/stat file.  All  of  the numbers reported  in  this file are  aggregates
1299since the system first booted.  For a quick look, simply cat the file:
1301  > cat /proc/stat
1302  cpu  2255 34 2290 22625563 6290 127 456 0 0 0
1303  cpu0 1132 34 1441 11311718 3675 127 438 0 0 0
1304  cpu1 1123 0 849 11313845 2614 0 18 0 0 0
1305  intr 114930548 113199788 3 0 5 263 0 4 [... lots more numbers ...]
1306  ctxt 1990473
1307  btime 1062191376
1308  processes 2915
1309  procs_running 1
1310  procs_blocked 0
1311  softirq 183433 0 21755 12 39 1137 231 21459 2263
1313The very first  "cpu" line aggregates the  numbers in all  of the other "cpuN"
1314lines.  These numbers identify the amount of time the CPU has spent performing
1315different kinds of work.  Time units are in USER_HZ (typically hundredths of a
1316second).  The meanings of the columns are as follows, from left to right:
1318- user: normal processes executing in user mode
1319- nice: niced processes executing in user mode
1320- system: processes executing in kernel mode
1321- idle: twiddling thumbs
1322- iowait: waiting for I/O to complete
1323- irq: servicing interrupts
1324- softirq: servicing softirqs
1325- steal: involuntary wait
1326- guest: running a normal guest
1327- guest_nice: running a niced guest
1329The "intr" line gives counts of interrupts  serviced since boot time, for each
1330of the  possible system interrupts.   The first  column  is the  total of  all
1331interrupts serviced  including  unnumbered  architecture specific  interrupts;
1332each  subsequent column is the  total for that particular numbered interrupt.
1333Unnumbered interrupts are not shown, only summed into the total.
1335The "ctxt" line gives the total number of context switches across all CPUs.
1337The "btime" line gives  the time at which the  system booted, in seconds since
1338the Unix epoch.
1340The "processes" line gives the number  of processes and threads created, which
1341includes (but  is not limited  to) those  created by  calls to the  fork() and
1342clone() system calls.
1344The "procs_running" line gives the total number of threads that are
1345running or ready to run (i.e., the total number of runnable threads).
1347The   "procs_blocked" line gives  the  number of  processes currently blocked,
1348waiting for I/O to complete.
1350The "softirq" line gives counts of softirqs serviced since boot time, for each
1351of the possible system softirqs. The first column is the total of all
1352softirqs serviced; each subsequent column is the total for that particular
13561.9 Ext4 file system parameters
1359Information about mounted ext4 file systems can be found in
1360/proc/fs/ext4.  Each mounted filesystem will have a directory in
1361/proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or
1362/proc/fs/ext4/dm-0).   The files in each per-device directory are shown
1363in Table 1-12, below.
1365Table 1-12: Files in /proc/fs/ext4/<devname>
1367 File            Content                                        
1368 mb_groups       details of multiblock allocator buddy cache of free blocks
13712.0 /proc/consoles
1373Shows registered system console lines.
1375To see which character device lines are currently used for the system console
1376/dev/console, you may simply look into the file /proc/consoles:
1378  > cat /proc/consoles
1379  tty0                 -WU (ECp)       4:7
1380  ttyS0                -W- (Ep)        4:64
1382The columns are:
1384  device               name of the device
1385  operations           R = can do read operations
1386                       W = can do write operations
1387                       U = can do unblank
1388  flags                E = it is enabled
1389                       C = it is preferred console
1390                       B = it is primary boot console
1391                       p = it is used for printk buffer
1392                       b = it is not a TTY but a Braille device
1393                       a = it is safe to use when cpu is offline
1394  major:minor          major and minor number of the device separated by a colon
1399The /proc file system serves information about the running system. It not only
1400allows access to process data but also allows you to request the kernel status
1401by reading files in the hierarchy.
1403The directory  structure  of /proc reflects the types of information and makes
1404it easy, if not obvious, where to look for specific data.
1412In This Chapter
1414* Modifying kernel parameters by writing into files found in /proc/sys
1415* Exploring the files which modify certain parameters
1416* Review of the /proc/sys file tree
1420A very  interesting part of /proc is the directory /proc/sys. This is not only
1421a source  of  information,  it also allows you to change parameters within the
1422kernel. Be  very  careful  when attempting this. You can optimize your system,
1423but you  can  also  cause  it  to  crash.  Never  alter kernel parameters on a
1424production system.  Set  up  a  development machine and test to make sure that
1425everything works  the  way  you want it to. You may have no alternative but to
1426reboot the machine once an error has been made.
1428To change  a  value,  simply  echo  the new value into the file. An example is
1429given below  in the section on the file system data. You need to be root to do
1430this. You  can  create  your  own  boot script to perform this every time your
1431system boots.
1433The files  in /proc/sys can be used to fine tune and monitor miscellaneous and
1434general things  in  the operation of the Linux kernel. Since some of the files
1435can inadvertently  disrupt  your  system,  it  is  advisable  to  read  both
1436documentation and  source  before actually making adjustments. In any case, be
1437very careful  when  writing  to  any  of these files. The entries in /proc may
1438change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt
1439review the kernel documentation in the directory /usr/src/linux/Documentation.
1440This chapter  is  heavily  based  on the documentation included in the pre 2.2
1441kernels, and became part of it in version 2.2.1 of the Linux kernel.
1443Please see: Documentation/sysctl/ directory for descriptions of these
1449Certain aspects  of  kernel  behavior  can be modified at runtime, without the
1450need to  recompile  the kernel, or even to reboot the system. The files in the
1451/proc/sys tree  can  not only be read, but also modified. You can use the echo
1452command to write value into these files, thereby changing the default settings
1453of the kernel.
14603.1 /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj- Adjust the oom-killer score
1463These file can be used to adjust the badness heuristic used to select which
1464process gets killed in out of memory conditions.
1466The badness heuristic assigns a value to each candidate task ranging from 0
1467(never kill) to 1000 (always kill) to determine which process is targeted.  The
1468units are roughly a proportion along that range of allowed memory the process
1469may allocate from based on an estimation of its current memory and swap use.
1470For example, if a task is using all allowed memory, its badness score will be
14711000.  If it is using half of its allowed memory, its score will be 500.
1473There is an additional factor included in the badness score: the current memory
1474and swap usage is discounted by 3% for root processes.
1476The amount of "allowed" memory depends on the context in which the oom killer
1477was called.  If it is due to the memory assigned to the allocating task's cpuset
1478being exhausted, the allowed memory represents the set of mems assigned to that
1479cpuset.  If it is due to a mempolicy's node(s) being exhausted, the allowed
1480memory represents the set of mempolicy nodes.  If it is due to a memory
1481limit (or swap limit) being reached, the allowed memory is that configured
1482limit.  Finally, if it is due to the entire system being out of memory, the
1483allowed memory represents all allocatable resources.
1485The value of /proc/<pid>/oom_score_adj is added to the badness score before it
1486is used to determine which task to kill.  Acceptable values range from -1000
1487(OOM_SCORE_ADJ_MIN) to +1000 (OOM_SCORE_ADJ_MAX).  This allows userspace to
1488polarize the preference for oom killing either by always preferring a certain
1489task or completely disabling it.  The lowest possible value, -1000, is
1490equivalent to disabling oom killing entirely for that task since it will always
1491report a badness score of 0.
1493Consequently, it is very simple for userspace to define the amount of memory to
1494consider for each task.  Setting a /proc/<pid>/oom_score_adj value of +500, for
1495example, is roughly equivalent to allowing the remainder of tasks sharing the
1496same system, cpuset, mempolicy, or memory controller resources to use at least
149750% more memory.  A value of -500, on the other hand, would be roughly
1498equivalent to discounting 50% of the task's allowed memory from being considered
1499as scoring against the task.
1501For backwards compatibility with previous kernels, /proc/<pid>/oom_adj may also
1502be used to tune the badness score.  Its acceptable values range from -16
1503(OOM_ADJUST_MIN) to +15 (OOM_ADJUST_MAX) and a special value of -17
1504(OOM_DISABLE) to disable oom killing entirely for that task.  Its value is
1505scaled linearly with /proc/<pid>/oom_score_adj.
1507The value of /proc/<pid>/oom_score_adj may be reduced no lower than the last
1508value set by a CAP_SYS_RESOURCE process. To reduce the value any lower
1509requires CAP_SYS_RESOURCE.
1511Caveat: when a parent task is selected, the oom killer will sacrifice any first
1512generation children with separate address spaces instead, if possible.  This
1513avoids servers and important system daemons from being killed and loses the
1514minimal amount of work.
15173.2 /proc/<pid>/oom_score - Display current oom-killer score
1520This file can be used to check the current score used by the oom-killer is for
1521any given <pid>. Use it together with /proc/<pid>/oom_score_adj to tune which
1522process should be killed in an out-of-memory situation.
15253.3  /proc/<pid>/io - Display the IO accounting fields
1528This file contains IO statistics for each running process
1533test:/tmp # dd if=/dev/zero of=/tmp/test.dat &
1534[1] 3828
1536test:/tmp # cat /proc/3828/io
1537rchar: 323934931
1538wchar: 323929600
1539syscr: 632687
1540syscw: 632675
1541read_bytes: 0
1542write_bytes: 323932160
1543cancelled_write_bytes: 0
1552I/O counter: chars read
1553The number of bytes which this task has caused to be read from storage. This
1554is simply the sum of bytes which this process passed to read() and pread().
1555It includes things like tty IO and it is unaffected by whether or not actual
1556physical disk IO was required (the read might have been satisfied from
1563I/O counter: chars written
1564The number of bytes which this task has caused, or shall cause to be written
1565to disk. Similar caveats apply here as with rchar.
1571I/O counter: read syscalls
1572Attempt to count the number of read I/O operations, i.e. syscalls like read()
1573and pread().
1579I/O counter: write syscalls
1580Attempt to count the number of write I/O operations, i.e. syscalls like
1581write() and pwrite().
1587I/O counter: bytes read
1588Attempt to count the number of bytes which this process really did cause to
1589be fetched from the storage layer. Done at the submit_bio() level, so it is
1590accurate for block-backed filesystems. <please add status regarding NFS and
1591CIFS at a later time>
1597I/O counter: bytes written
1598Attempt to count the number of bytes which this process caused to be sent to
1599the storage layer. This is done at page-dirtying time.
1605The big inaccuracy here is truncate. If a process writes 1MB to a file and
1606then deletes the file, it will in fact perform no writeout. But it will have
1607been accounted as having caused 1MB of write.
1608In other words: The number of bytes which this process caused to not happen,
1609by truncating pagecache. A task can cause "negative" IO too. If this task
1610truncates some dirty pagecache, some IO which another task has been accounted
1611for (in its write_bytes) will not be happening. We _could_ just subtract that
1612from the truncating task's write_bytes, but there is information loss in doing
1619At its current implementation state, this is a bit racy on 32-bit machines: if
1620process A reads process B's /proc/pid/io while process B is updating one of
1621those 64-bit counters, process A could see an intermediate result.
1624More information about this can be found within the taskstats documentation in
16273.4 /proc/<pid>/coredump_filter - Core dump filtering settings
1629When a process is dumped, all anonymous memory is written to a core file as
1630long as the size of the core file isn't limited. But sometimes we don't want
1631to dump some memory segments, for example, huge shared memory or DAX.
1632Conversely, sometimes we want to save file-backed memory segments into a core
1633file, not only the individual files.
1635/proc/<pid>/coredump_filter allows you to customize which memory segments
1636will be dumped when the <pid> process is dumped. coredump_filter is a bitmask
1637of memory types. If a bit of the bitmask is set, memory segments of the
1638corresponding memory type are dumped, otherwise they are not dumped.
1640The following 9 memory types are supported:
1641  - (bit 0) anonymous private memory
1642  - (bit 1) anonymous shared memory
1643  - (bit 2) file-backed private memory
1644  - (bit 3) file-backed shared memory
1645  - (bit 4) ELF header pages in file-backed private memory areas (it is
1646            effective only if the bit 2 is cleared)
1647  - (bit 5) hugetlb private memory
1648  - (bit 6) hugetlb shared memory
1649  - (bit 7) DAX private memory
1650  - (bit 8) DAX shared memory
1652  Note that MMIO pages such as frame buffer are never dumped and vDSO pages
1653  are always dumped regardless of the bitmask status.
1655  Note that bits 0-4 don't affect hugetlb or DAX memory. hugetlb memory is
1656  only affected by bit 5-6, and DAX is only affected by bits 7-8.
1658The default value of coredump_filter is 0x33; this means all anonymous memory
1659segments, ELF header pages and hugetlb private memory are dumped.
1661If you don't want to dump all shared memory segments attached to pid 1234,
1662write 0x31 to the process's proc file.
1664  $ echo 0x31 > /proc/1234/coredump_filter
1666When a new process is created, the process inherits the bitmask status from its
1667parent. It is useful to set up coredump_filter before the program runs.
1668For example:
1670  $ echo 0x7 > /proc/self/coredump_filter
1671  $ ./some_program
16733.5     /proc/<pid>/mountinfo - Information about mounts
1676This file contains lines of the form:
167836 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
1679(1)(2)(3)   (4)   (5)      (6)      (7)   (8) (9)   (10)         (11)
1681(1) mount ID:  unique identifier of the mount (may be reused after umount)
1682(2) parent ID:  ID of parent (or of self for the top of the mount tree)
1683(3) major:minor:  value of st_dev for files on filesystem
1684(4) root:  root of the mount within the filesystem
1685(5) mount point:  mount point relative to the process's root
1686(6) mount options:  per mount options
1687(7) optional fields:  zero or more fields of the form "tag[:value]"
1688(8) separator:  marks the end of the optional fields
1689(9) filesystem type:  name of filesystem of the form "type[.subtype]"
1690(10) mount source:  filesystem specific information or "none"
1691(11) super options:  per super block options
1693Parsers should ignore all unrecognised optional fields.  Currently the
1694possible optional fields are:
1696shared:X  mount is shared in peer group X
1697master:X  mount is slave to peer group X
1698propagate_from:X  mount is slave and receives propagation from peer group X (*)
1699unbindable  mount is unbindable
1701(*) X is the closest dominant peer group under the process's root.  If
1702X is the immediate master of the mount, or if there's no dominant peer
1703group under the same root, then only the "master:X" field is present
1704and not the "propagate_from:X" field.
1706For more information on mount propagation see:
1708  Documentation/filesystems/sharedsubtree.txt
17113.6     /proc/<pid>/comm  & /proc/<pid>/task/<tid>/comm
1713These files provide a method to access a tasks comm value. It also allows for
1714a task to set its own or one of its thread siblings comm value. The comm value
1715is limited in size compared to the cmdline value, so writing anything longer
1716then the kernel's TASK_COMM_LEN (currently 16 chars) will result in a truncated
1717comm value.
17203.7     /proc/<pid>/task/<tid>/children - Information about task children
1722This file provides a fast way to retrieve first level children pids
1723of a task pointed by <pid>/<tid> pair. The format is a space separated
1724stream of pids.
1726Note the "first level" here -- if a child has own children they will
1727not be listed here, one needs to read /proc/<children-pid>/task/<tid>/children
1728to obtain the descendants.
1730Since this interface is intended to be fast and cheap it doesn't
1731guarantee to provide precise results and some children might be
1732skipped, especially if they've exited right after we printed their
1733pids, so one need to either stop or freeze processes being inspected
1734if precise results are needed.
17373.8     /proc/<pid>/fdinfo/<fd> - Information about opened file
1739This file provides information associated with an opened file. The regular
1740files have at least three fields -- 'pos', 'flags' and mnt_id. The 'pos'
1741represents the current offset of the opened file in decimal form [see lseek(2)
1742for details], 'flags' denotes the octal O_xxx mask the file has been
1743created with [see open(2) for details] and 'mnt_id' represents mount ID of
1744the file system containing the opened file [see 3.5 /proc/<pid>/mountinfo
1745for details].
1747A typical output is
1749        pos:    0
1750        flags:  0100002
1751        mnt_id: 19
1753All locks associated with a file descriptor are shown in its fdinfo too.
1755lock:       1: FLOCK  ADVISORY  WRITE 359 00:13:11691 0 EOF
1757The files such as eventfd, fsnotify, signalfd, epoll among the regular pos/flags
1758pair provide additional information particular to the objects they represent.
1760        Eventfd files
1761        ~~~~~~~~~~~~~
1762        pos:    0
1763        flags:  04002
1764        mnt_id: 9
1765        eventfd-count:  5a
1767        where 'eventfd-count' is hex value of a counter.
1769        Signalfd files
1770        ~~~~~~~~~~~~~~
1771        pos:    0
1772        flags:  04002
1773        mnt_id: 9
1774        sigmask:        0000000000000200
1776        where 'sigmask' is hex value of the signal mask associated
1777        with a file.
1779        Epoll files
1780        ~~~~~~~~~~~
1781        pos:    0
1782        flags:  02
1783        mnt_id: 9
1784        tfd:        5 events:       1d data: ffffffffffffffff
1786        where 'tfd' is a target file descriptor number in decimal form,
1787        'events' is events mask being watched and the 'data' is data
1788        associated with a target [see epoll(7) for more details].
1790        Fsnotify files
1791        ~~~~~~~~~~~~~~
1792        For inotify files the format is the following
1794        pos:    0
1795        flags:  02000000
1796        inotify wd:3 ino:9e7e sdev:800013 mask:800afce ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:7e9e0000640d1b6d
1798        where 'wd' is a watch descriptor in decimal form, ie a target file
1799        descriptor number, 'ino' and 'sdev' are inode and device where the
1800        target file resides and the 'mask' is the mask of events, all in hex
1801        form [see inotify(7) for more details].
1803        If the kernel was built with exportfs support, the path to the target
1804        file is encoded as a file handle.  The file handle is provided by three
1805        fields 'fhandle-bytes', 'fhandle-type' and 'f_handle', all in hex
1806        format.
1808        If the kernel is built without exportfs support the file handle won't be
1809        printed out.
1811        If there is no inotify mark attached yet the 'inotify' line will be omitted.
1813        For fanotify files the format is
1815        pos:    0
1816        flags:  02
1817        mnt_id: 9
1818        fanotify flags:10 event-flags:0
1819        fanotify mnt_id:12 mflags:40 mask:38 ignored_mask:40000003
1820        fanotify ino:4f969 sdev:800013 mflags:0 mask:3b ignored_mask:40000000 fhandle-bytes:8 fhandle-type:1 f_handle:69f90400c275b5b4
1822        where fanotify 'flags' and 'event-flags' are values used in fanotify_init
1823        call, 'mnt_id' is the mount point identifier, 'mflags' is the value of
1824        flags associated with mark which are tracked separately from events
1825        mask. 'ino', 'sdev' are target inode and device, 'mask' is the events
1826        mask and 'ignored_mask' is the mask of events which are to be ignored.
1827        All in hex format. Incorporation of 'mflags', 'mask' and 'ignored_mask'
1828        does provide information about flags and mask used in fanotify_mark
1829        call [see fsnotify manpage for details].
1831        While the first three lines are mandatory and always printed, the rest is
1832        optional and may be omitted if no marks created yet.
1834        Timerfd files
1835        ~~~~~~~~~~~~~
1837        pos:    0
1838        flags:  02
1839        mnt_id: 9
1840        clockid: 0
1841        ticks: 0
1842        settime flags: 01
1843        it_value: (0, 49406829)
1844        it_interval: (1, 0)
1846        where 'clockid' is the clock type and 'ticks' is the number of the timer expirations
1847        that have occurred [see timerfd_create(2) for details]. 'settime flags' are
1848        flags in octal form been used to setup the timer [see timerfd_settime(2) for
1849        details]. 'it_value' is remaining time until the timer exiration.
1850        'it_interval' is the interval for the timer. Note the timer might be set up
1851        with TIMER_ABSTIME option which will be shown in 'settime flags', but 'it_value'
1852        still exhibits timer's remaining time.
18543.9     /proc/<pid>/map_files - Information about memory mapped files
1856This directory contains symbolic links which represent memory mapped files
1857the process is maintaining.  Example output:
1859     | lr-------- 1 root root 64 Jan 27 11:24 333c600000-333c620000 -> /usr/lib64/
1860     | lr-------- 1 root root 64 Jan 27 11:24 333c81f000-333c820000 -> /usr/lib64/
1861     | lr-------- 1 root root 64 Jan 27 11:24 333c820000-333c821000 -> /usr/lib64/
1862     | ...
1863     | lr-------- 1 root root 64 Jan 27 11:24 35d0421000-35d0422000 -> /usr/lib64/
1864     | lr-------- 1 root root 64 Jan 27 11:24 400000-41a000 -> /usr/bin/ls
1866The name of a link represents the virtual memory bounds of a mapping, i.e.
1869The main purpose of the map_files is to retrieve a set of memory mapped
1870files in a fast way instead of parsing /proc/<pid>/maps or
1871/proc/<pid>/smaps, both of which contain many more records.  At the same
1872time one can open(2) mappings from the listings of two processes and
1873comparing their inode numbers to figure out which anonymous memory areas
1874are actually shared.
18763.10    /proc/<pid>/timerslack_ns - Task timerslack value
1878This file provides the value of the task's timerslack value in nanoseconds.
1879This value specifies a amount of time that normal timers may be deferred
1880in order to coalesce timers and avoid unnecessary wakeups.
1882This allows a task's interactivity vs power consumption trade off to be
1885Writing 0 to the file will set the tasks timerslack to the default value.
1887Valid values are from 0 - ULLONG_MAX
1889An application setting the value must have PTRACE_MODE_ATTACH_FSCREDS level
1890permissions on the task specified to change its timerslack_ns value.
1894Configuring procfs
18974.1     Mount options
1900The following mount options are supported:
1902        hidepid=        Set /proc/<pid>/ access mode.
1903        gid=            Set the group authorized to learn processes information.
1905hidepid=0 means classic mode - everybody may access all /proc/<pid>/ directories
1908hidepid=1 means users may not access any /proc/<pid>/ directories but their
1909own.  Sensitive files like cmdline, sched*, status are now protected against
1910other users.  This makes it impossible to learn whether any user runs
1911specific program (given the program doesn't reveal itself by its behaviour).
1912As an additional bonus, as /proc/<pid>/cmdline is unaccessible for other users,
1913poorly written programs passing sensitive information via program arguments are
1914now protected against local eavesdroppers.
1916hidepid=2 means hidepid=1 plus all /proc/<pid>/ will be fully invisible to other
1917users.  It doesn't mean that it hides a fact whether a process with a specific
1918pid value exists (it can be learned by other means, e.g. by "kill -0 $PID"),
1919but it hides process' uid and gid, which may be learned by stat()'ing
1920/proc/<pid>/ otherwise.  It greatly complicates an intruder's task of gathering
1921information about running processes, whether some daemon runs with elevated
1922privileges, whether other user runs some sensitive program, whether other users
1923run any program at all, etc.
1925gid= defines a group authorized to learn processes information otherwise
1926prohibited by hidepid=.  If you use some daemon like identd which needs to learn
1927information about processes information, just add identd to this group.
1928 kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.